Friction type draft gear assemblies are widely used in United States railroad industry to provide protection to a railway car by absorbing shocks in both draft and buff conditions must meet various Association of American Railroads (AAR) requirements. In one aspect, draft gear must be capable of maintaining the minimum shock absorbing capacity during its service life required by AAR standard M-901-G to be at least 36,000 foot pounds being measured during a drop hammer test. In the other aspect, AAR mandates working action of such draft gear to be achieved without exceeding a 500,000 pound reaction pressure acting on the freight car sills in order to prevent upsetting the coupler shank. In a further aspect, the draft gear must fit into a standard railway car pocket of 24.62 inches in length.
U.S. Pat. Nos. 5,152,409, 5,590,797 and 3,368,698, all owned by assignee of the present invention and hereby incorporated by reference thereto, relate to commonly used friction draft gears, which are installed in alignment with a railway car center sill having a pair of front stops and a pair of rear stops. Such draft gears include a housing fitting entirely between the front and rear stops and having an open front portion disposed adjacent a pair of front stops and a closed rear portion which engages a pair of rear stops. A compressible cushioning element is positioned within the rear portion of the housing. A friction cushioning element is adopted in the front portion of the housing. The draft gears further include a spring release mechanism for continuously urging the friction cushioning element outwardly from the compressible cushioning element thereby releasing such friction cushioning element after compression of such draft gears. The compressible cushioning element is typically either of an all spring configuration as taught in U.S. Pat. Nos. 5,152,409 and 5,590,797 or of a spring and hydraulic assembly combination as taught in U.S. Pat. No. 3,368,698.
It is now known that certain railroads require a higher protection to the railway car by allowing an extended travel of about 4.75 inches in order to meet the requirements. At the same time, the draft gear with such extended travel must fit within the identical draft gear pocket length of 24.625 inches as the draft gears presently in use which are capable to travel only 3.25 inches.